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What ails our industry – Part VI

In this, the concluding article of a six-part series, George Berbari looks at radiant cooling systems as an attractive option, considering they help save on costs associated with air-handling unit, ducting, filtration, fan and chiller energy

Chilled beams, active chilled beams and underfloor radiant cooling are still being used in niche upscale markets, where the price of chilled beams ranges between USD 1,000 and USD 2,000 per tonne of refrigeration (TR). They require a chilled water supply temperature of 57 to 60 degrees F (14 to 16 degrees C) to avoid condensation.

Radiant systems are better designed with small dedicated chillers that directly supply the desired temperatures for radiant cooling. The systems avoid large pumping losses, as they require two to three times the chilled water flow of traditional systems, owing to low chilled water ΔT of 5.4 to 7.2 degrees F (3 to 4 degrees C), as compared to 10 to 16 degrees F (5.6 to 8.9 degrees C) for traditional systems.

Radiant systems can be installed under the tiles with a five-centimetre polystyrene insulation under 200mm-diameter PEX or HDPE pipes, and can be protected by light-weight concrete screed. They typically can deliver up to 50 watts/m2 or 70m2/TR, which can cover around 50% of the cooling needs typically requiring 80 to 100 watts/m2 or 35 to 42m2/TR. If used alone, they need to be complemented by another source of cooling, such as a fan-coil unit or an air-handling unit.

Radiant cooling systems could be put above the roof slab with insulation and water proofing above them. Some people embed them in the concrete slab and lay them in the steel reinforcement and test them prior to pouring the concrete.

Another type of radiant cooling is wall-based. Such a system is less-frequently installed, as it raises concerns when put behind a gypsum board, as the occupant might drill the wall, causing damage to the pipe behind it.

One application where air distribution is very expensive and dangerous is in the healthcare sector, as it may distribute bacteria, viruses and diseases. Imagine a hospital room with radiant cooling, though, and a small fresh air and exhaust duct, used for ventilation, with no cross-contaminating wheel but with liquid desiccant heat recovery. I call an all-radiant-cooling hospital a dream application, because it can save capital cost, operating cost and precious space that would otherwise be taken by air-handling units and large ducts.

Applications include large halls at the new Muscat International Airport MC3, in Oman; the Louvre Museum, Yas Island Yacht Club and the Sheikh Zayed Desert Learning Center, all in the UAE; the Royal Clock Tower, in Makkah, Saudi Arabia, and the Banana Island Resort, in Doha, Qatar.

Radiant cooling systems will work famously well, if all possible pitfalls are avoided. For instance, a common mistake is to take chilled water from a District Cooling scheme or a central chilled water air conditioning system at 42 to 45 degrees F (5.5 or 7 degrees C) and pass it through a three-way control valve or heat exchanger to raise the supply temperature for the radiant systems. I classify it as a common mistake, because it amounts to wasting most of the energy-saving benefits achieved in the compressor by supplying higher chilled water temperature.

Overall, great care needs to be taken while deploying radiant cooling systems. It is essential to conduct a detailed feasibility study and to collect trial samples with field measurement and third-party certification prior to implementation. It makes sense to go through a process of due diligence, as we are talking of a new industry, which while is well established in the heating market, is trying to expand into the cooling industry.

Conclusion

This is the sixth and the concluding part of a “harangue”. The manner in which I chose to express my views stems from my love for the HVAC industry and my sense of anguish when confronted with poor practices.

The GCC region is under enormous pressure, as a result of a five to 10% annual increase in power consumption; the HVAC industry is contributing to half of the annual consumption, and 60 to 65% of the power demand. With these facts, shouldn’t the HVAC industry stand up and lead conservation efforts, instead of purely focusing on the business side?

The industry has to wake up and strongly engage with government authorities and utilities, as they take efforts to spread renewables and energy conservation. It is upon the HVAC industry to provide better alternatives to the systems being used today. I have seen the industry resisting more stringent regulation and guiding the government into leaner regulation, based on consensus.

I am hopeful my outcry will start a serious discussion and trigger a change to the status quo; as a responsible stakeholder, I will strive for that change to happen – and quickly, at that.

The indirect-direct combo

Though the focus of the article has been on radiant cooling, I could not resist talking about the interesting developments surrounding evaporative cooling. We are witness to a new approach – an indirect evaporative cooling regimen, followed by direct evaporative cooling – finding its way into the market.

In peak summer, evaporative cooling can deliver air at 35 to 38 degrees C in the coastal areas of the GCC region and at 27 to 29 degrees C in dry areas, such as Riyadh, Madinah and Baghdad. A combination of indirect and direct evaporative cooling can deliver air at 28 to 31 degrees C in the coastal areas and at 19 to 21 degrees C in dry areas. The combination could resolve outdoor cooling in coastal areas and open new cooling applications in dry areas.